This invention relates to a hydraulic control system for a sidewall coring tool. In determining the physical properties of subterranean formations, it is of great assistance to have what is commonly called cores. A core is typically a cylindrical piece of rock which has been cut from an underground formation and can vary in size and length. A typical size is 1/2 in. diameter and 4 to 6 in. long, although samples can be of larger diameter and of greater length depending upon the facilities available. One type of core cutter is a type that can be used to cut the cores from the sidewall of a borehole after the borehole has already been drilled. Such a sidewall coring tool is described in U.S. Pat. No. 4,280,569, entitled "Fluid Flow Restrictor Valve for a Drill Hole Coring Tool", issued July 28, 1981, to Houston B. Mount, II., inventor. In that invention, a core barrel having a core bit on the end thereof, is pushed against the formation at the same time the core barrel is being rotated so that as the core is cut it enters into the core barrel. A high volume hydraulic system is used to rotate a hydraulic motor which, in turn, rotates the core cutting bit. A low volume hydraulic system is used to force the drill bit against the formation. Control means are provided so that if the torque on the hydraulic motor, used to rotate the bit, increases, the pressure of the fluid which is used to force the bit against the wall is reduced. On the other hand, if the torque decreases on the hydraulic drive motor for the bit, the pressure of the hydraulic fluid on the means forcing the core bit against the formation increases. Thus, the control system is designed to prevent the hydraulic motor from being over torqued by being advanced too rapidly into the formation. A problem that has arisen in the operation of this type of system is that torque compensating adjustments of the automatic drilling hydraulic circuit are very sensitive to changes in ambient temperatures in the wellbore. The present invention overcomes this problem.